Oxygen – Haemoglobin Dissociation Curve – Physiology
10
October

By Adem Lewis / in , , , , , , , , , , , , , , , , , , , /


Hello, in this
video, we’re going to focus on lung physiology,
focusing on gases and pH. And we’ll also look at the
oxygen dissociation curve. So air enters the respiratory
system in the upper airways, proceeds to the
conducting airways and then onto the
respiratory airways made up of the branches of the bronchi,
bronchial, terminal bronchioles and finally ends in the alveoli. You can think of the alveolarus,
which is singular of alveoli, as the building blocks
of the lungs where gas exchange occurs– gas exchange occurring between
the lungs and the bloodstream. The gas exchange in this case
is between oxygen and carbon dioxide, or CO2. So just recapping,
the basic physiology– the heart will pump
deoxygenated blood from the right ventricle
towards the lungs. deoxygenated blood means
blood containing a higher concentration of CO2 with
lower amounts of oxygen. In each alveolus, the carbon
dioxide will be dropped off and exhaled out of the body,
so removing carbon dioxide from a body. And then oxygen will be
inhaled and will then reoxygenate the blood. This newly oxygenated
blood or reoxygenated blood will then go back to the
left side of the heart. The heart will then pump
this oxygenated blood around the body to the other
organs, such as the brain. The deoxygenated blood delivers
oxygen to organs, tissues. The organ tissues then
uses up this oxygen to help create energy
in the form of ATP. Now as a process of creating
this energy ATP, the organs, the tissues will
form a byproduct, which is carbon dioxide. Carbon dioxide is then
made and is actually expelled into the bloodstream
as exchange, you can say. Now because carbon dioxide
is in the bloodstream, the blood is now
deoxygenated once again. And this deoxygenated
blood will return to the right side of the heart. The right side of the heart
will continue this cycle. It will pump blood to the
lungs to reoxygenate the blood. Oxygen itself travels in the
body mainly in red blood cells. Oxygen binds to these
molecules called hemoglobin, and we have millions of
these in each red blood cell. In deoxygenated blood, with
deoxygenated hemoglobin, or deoxyhemoglobin, the
structure of hemoglobin here is referred to
as a tight structure. Hemoglobin– just recapping– is a protein made up of
four subunits, each of which contain a heme [INAUDIBLE]
attached to a globin chain. And each globin chain contains
iron where oxygen normally binds to. Each of the four iron
atoms in hemoglobin can reversibly bind
one oxygen molecule. Let’s see what happens when
deoxyhemoglobin receives oxygen. Well, the
reaction is rapid, requiring less
than 0.01 seconds. Remember in deoxyhemoglobin,
the globin units are tightly bound in
a tense configuration, in a t configuration, which
means that it actually reduces the affinity of
the molecule for oxygen. When oxygen is first bound, the
bonds holding the globin units are released, producing a
relaxed configuration, or an r configuration, which exposes
more oxygen binding sites. So to put it simply, you
can imagine it like cascade. Firstly, the hemoglobin is
in a tense configuration with no oxygen. And then
when oxygen starts to bind, it will become more relaxed,
a relaxed configuration, which actually increases the
affinity for oxygen even more– kind of weird. This whole thing is called
positive cooperativity. So by the end, the hemoglobin
molecule is oxyhemoglobin, because it is
filled with oxygen. And it is in a relaxed form. So from the lungs,
you now have heaps of oxyhemoglobin, which means
your blood is reoxygenated really. And this reoxygenated
blood is ready to be delivered to the body tissues. It’s a good idea
now to briefly talk about partial pressures of
oxygen and carbon dioxide in deoxygenated blood and
also in oxygenated blood, because it will be relevant to
what we’ll talk about later. But you can imagine that
when blood is oxygenated or reoxygenated
from the lungs, it would have a higher partial
pressure of oxygen, so higher amounts of oxygen, 100. And carbon dioxide is low, 40. The deoxygenated blood
I am talking about are found in your arteries,
such as your aorta. Deoxygenated blood, on the
other hand, is very different. When we talk about
deoxygenated blood, we are talking about the veins. So oxygen can be up to 40
millimeters mercury and carbon dioxide about 45. The changes in
partial pressure is important to understand because
it helps explain the hemoglobin dissociation curve. And we will talk about that now. The hemoglobin dissociation
curve, or the oxygen hemoglobin dissociation curve, relates
a percentage saturation of the oxygen carrying
power of hemoglobin to the partial
pressure of oxygen. Now that might sound
crazy, but let’s just try to understand it together. So on the x-axis, you
have the partial pressure of oxygen, 25 to 100
millimeters of mercury. And on the y-axis, you
have the saturation of hemoglobin, which what
we’re looking at specifically is oxyhemoglobin in percentage. This saturation of
hemoglobin means how much oxygen is bound to
the hemoglobin basically. The more oxygen
bound to hemoglobin, the higher the
oxyhemoglobin and therefore, the higher the saturation. So the oxygen hemoglobin
dissociation curve has a characteristic
sigmoid shape due to the tense and relaxed
configuration inter-conversion. There is a plateau here where
the partial pressure of oxygen is nearly high. The plateau signifies that
high partial pressure of oxygen does not cause large
changes in oxygen saturation of hemoglobin. So at the plateau, you can
see that the partial pressure of oxygen of 100 already has
an oxygen saturation of 98%. So there is not much change
whereas before the plateau– so a partial pressure of
oxygen or 50, let’s just say, already has an oxygen saturation
of 85%, so a dramatic change. So note that small changes at
low partial oxygen pressure leads to large changes
in oxygen saturation. Another example is that a low
partial pressure of oxygen, such as 26, has already
oxygen saturation of 50%. The reason for
this sigmoid shape and why a low partial
pressure of oxygen has a quick increase
in oxygen saturation is because of positive
cooperativity When the first heme in the
hemoglobin molecule receives oxygen, the affinity
increases for the second and the third, and so on. Now let’s look at factors which
can shift this curve, which are essentially
factors affecting the affinity of
hemoglobin for oxygen. Three important conditions
affect the oxygen hemoglobin dissociation curve. These are the pH,
the temperature, and the concentration of 2,
3-diphosphateglycerate, or DPG. Here is the curve normally. We will look at examples of what
shifts the curve to the right and what shifts the
curve to the left. When the curve
shifts to the right, it means that there is reduced
hemoglobin oxygen affinity. And this occurs in tissues. So basically, the hemoglobin
affinity for oxygen is decreased. Remember the normal curve,
the partial pressure of oxygen of 50 had an oxygen
saturation of about 83% to 85%. In this new curve, the partial
pressure of oxygen of 50 has an oxygen saturation of 70%,
so reduced oxygen saturation. And this is because there is
reduced affinity for oxygen. Things that cause this to
happen include an increase in carbon dioxide, which
really means a decrease in pH. Other things that causes
the shift to happen include an increase
in temperature and an increase in DPG, or BPG. It’s good to remember that
the reduced hemoglobin oxygen affinity occurs
in tissues in general. Because when you
think about it, you want to give your oxygen
to the body tissues so that they can use it. These tissues
include the placenta, because you want to offload
oxygen to the fetus, and muscles cells,
especially during exercise. Now the curve can also shift
to the left here in red. What happens here is that we
see higher hemoglobin oxygen affinity. And for this example, you
can think of the lungs, because it is in the lungs
where oxygen comes and binds to hemoglobin. And so you would expect
to see higher hemoglobin oxygen affinity here. Later when the blood
travels to the body tissues, such as the muscles,
the affinity reduces, as we have learned. The other factors
which contribute to the high hemoglobin oxygen
affinity, so this red curve, are reduced carbon dioxide,
which means higher pH, reduced temperature
and also reduced DPG, which is essentially
opposite to the curve when it shifts to the right. So let’s compare now. In this red curve, so a high
hemoglobin oxygen affinity, if the person has a partial
pressure of oxygen of 50, the oxygen saturation
is already 90%. So in this video,
we talked about how oxygen binds onto hemoglobin
from a deoxygenated state in a tense configuration into
a relaxed r configuration. And we also talked about the
oxygen dissociation curve and factors which caused the
curve to shift to the right, as well as factors which caused
the curve to shift to the left. Hope it made sense. Thank you for watching.


98 thoughts on “Oxygen – Haemoglobin Dissociation Curve – Physiology

  1. armando! we just went over hemoglobin-dissociation curves in a&p lecture today so the timing on this upload was perfect

  2. So, it's like the oxygen molecules act as protons that dissociate in acid base reactions. I find that interesting

  3. Hi ! French student here thanking you a lot for all your videos ! Just one question though, what does DPG means ?

  4. Great Explanation , Please make a video to show what is the role of water in our body , thanks in advance

  5. Amazing explanation!
    One tip to remember the factors affecting the dissociation curve is "CADET, face RIGHT!"
    C – CO2
    A – Acidity
    D – DPG
    E – Exercise
    T – Temperature
    Rise in all these shifts the curve to right.

    I hope it helps to all the readers!

  6. Ufff ur handwriting and diagram and color choice is soo good it makes me to watch ur video on and on and on……

  7. You didnt explain the 2,3 bis phosphoglycerate role
    How it shifts
    Is that so that in tissues glycolysis yields 2,3 bisphosphoglycerate.so affinity of HB decreases for oxygen hence it is delieverd to site
    Please clarify me

  8. Sorry to say this, hemoglobin will have only one iron in its structure may be ferrous or ferric.. it doesn't has 4 iron molecules to each oxygen … It has 4globin chains n 1 ferrous ion in its centre… It would have been nice if u linked oxygen n co2 transport in first half… First half is more over like explaining to non medical students with colorful diagrams… But odc is good… Tq

  9. So if there is a shift to the right does that mean that oxygen is more likely to be released from the hemoglobin to the tissues, and a shift to the left means the hemoglobin is more likely to hold onto the oxygen? And with that, does that also mean a right shift=less O2 pick up in lungs; left shift=less O2 to tissues?

  10. You having an amazing way of explaining the systems separately i have a test tomorrow and my science teacher has a false way of explaining things so thank you very much

  11. Important to remember that only a relatively small amount of CO2 is exhaled. Most CO2 stays in the blood. Venous blood CO2 is 45mmHg. arterial blood CO2 is 40mmHg. So only 5mmHg is exhaled.

  12. thank you , simple and well explained unlike guyton book
    in 1:40 did you mean oxygenated blood because i'm confused

  13. ขอบคุณค่ะ อธิบายดีจริงๆ
    Thank you very much.
    Good explanation this help me to my quiz

  14. Well done👍👍👍
    I think it would be nice to put a link to a HD picture of the whole drawings of every video of yours so that we can use them as flashcards

  15. Can you please upload the drawing to your website. I cant find it there. Thank you so much for the lecture

  16. Thanks for that video which is sure clear.
    Can you confirm that the ppO2 you are speaking about is arterial pressure? I'm still trying to fully understand the big picture of it due to the different ppO2 depending on body locations (alveorus, arterial, veins)

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